U.S. patent application number 13/597464 was filed with the patent office on 2012-12-20 for high viscosity heat sensitive ink printing process.
Invention is credited to Ming Xu.
Application Number | 20120320136 13/597464 |
Document ID | / |
Family ID | 43427144 |
Filed Date | 2012-12-20 |
United States Patent
Application |
20120320136 |
Kind Code |
A1 |
Xu; Ming |
December 20, 2012 |
HIGH VISCOSITY HEAT SENSITIVE INK PRINTING PROCESS
Abstract
A high viscosity aqueous inkjet ink that is useful in ink jet
printers. The ink comprises heat activated colorant solids that are
not heat activated during the printing process, and are printed
onto a substrate in the form of an image that can be transferred
onto a subsequent or final substrate by applying heat and intimate
contact between the two substrates. The ink can also be heat
activated onto the substrate without further transfer by applying
heat at the temperature that is suitable for the activation of the
colorant.
Inventors: |
Xu; Ming; (Malvern,
PA) |
Family ID: |
43427144 |
Appl. No.: |
13/597464 |
Filed: |
August 29, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12833383 |
Jul 9, 2010 |
|
|
|
13597464 |
|
|
|
|
61224720 |
Jul 10, 2009 |
|
|
|
Current U.S.
Class: |
347/95 |
Current CPC
Class: |
C09D 11/322 20130101;
B41J 2/17593 20130101; B41M 5/0023 20130101; B41J 2/2107 20130101;
C09D 11/02 20130101; B41M 7/009 20130101; C09D 11/328 20130101;
C09D 11/38 20130101 |
Class at
Publication: |
347/95 |
International
Class: |
B41J 2/17 20060101
B41J002/17 |
Claims
1. A method of printing a design by means of an ink jet printer
using heat activated colorant solids, comprising the steps of:
preparing a liquid ink suitable for use in an ink jet printer which
uses liquid ink, said liquid ink comprising water, heat activated
colorant solids, and a viscosity control agent comprising not less
than 15% by weight of the liquid ink, wherein the liquid ink has a
viscosity of not less than 6.0 centipoise, wherein the heat
activated colorant solids are sparingly soluble in the viscosity
control agent, and wherein an upper limit of a distribution of
particle sizes of particles of the heat activated colorant solids
is a function of both the smallest orifice of the print head of an
ink jet printer used to print the liquid ink and the ratio of the
total weight of the head activated colorant solids to the total
weight of the liquid ink; supplying the ink jet printer that prints
liquid ink with said liquid ink; printing said liquid ink in a
desired image by means of said ink jet printer on a substrate to
form an image, wherein the particles of the heat activated colorant
solids are solid at the time of printing; and heat activating the
heat activated colorant solids, wherein, after heat activation, the
image has an optical density of not less than 1.25 when measured by
an X-Rite densitometer.
2. A method of printing a design by means of an ink jet printer
using heat activated colorant solids, as described in claim 1,
wherein the ink jet printer is constructed to print liquid ink
having a viscosity of 5.0 centipoise or more.
3. A method of printing a design by means of an ink jet printer
using heat activated colorant solids, as described in claim 1,
wherein the viscosity control agent increases the liquid ink to a
viscosity of at least 6.0 centipoise and the weight of the
viscosity control agent present in a volume of heat activated ink
is at least three times the weight of the heat activated colorant
present in the volume of heat activated ink.
4. A method of printing a design by means of an ink jet printer
using heat activated colorant solids, as described in claim 1,
wherein the viscosity control agent is glycol and the glycol
increases the liquid ink to a viscosity of at least 6.0 centipoise
and the weight of the glycol present in a volume of heat activated
ink is at least three times the weight of the heat activated
colorant present in the volume of heat activated ink.
5. A method of printing a design by means of an ink jet printer
using heat activated colorant solids, as described in claim 1,
wherein the viscosity control agent increases the liquid ink to a
viscosity of at least 6.0 centipoise and the weight of the
viscosity control agent present in a volume of heat activated ink
is 15-60% of the total weight of the volume of heat activated
ink.
6. A method of printing a design by means of an ink jet printer
using heat activated colorant solids, as described in claim 1,
wherein the heat activation temperature of the colorant is not
substantially higher than the boiling point of the viscosity
control agent.
7. A method of printing a design by means of an ink jet printer
using heat activated colorant solids, as described in claim 1,
wherein the heat activation temperature of the colorant in not more
than 20 degrees Fahrenheit higher than the boiling point of the
viscosity control agent.
8. A method of printing a design by means of an ink jet printer
using heat activated colorant solids, as described in claim 1,
wherein substantially all particles of the colorant having a
diameter of less than 50 nanometers are excluded from the ink.
Description
[0001] This application is a divisional of pending application Ser.
No. 12/833,383 filed Jul. 9, 2010. Applicant Claims the benefit of
U.S. Provisional Application Ser. No. 61/224,720 filed Jul. 10,
2009, under 35 USC .sctn.119(e), from which pending application
Ser. No. 12/833,383 claimed priority.
FIELD OF THE INVENTION
[0002] This invention relates to a method of inkjet printing of
heat activated colorants and an ink comprising heat activated
colorants.
BACKGROUND OF THE INVENTION
[0003] Inkjet digital printing has been widely used in many
applications. Its refined image quality, comparing with
conventional analog technologies such as offset printing, screen
printing, lithographic printing, digital inkjet printing
technologies generate much convenient, efficient and
environmentally clean results.
[0004] However, aqueous digital printing on materials other than
paper may be inferior to other processes due to lack of color
intensity and speed due to some shortcomings of digital inkjet
printing methods. Among those, low viscosity, low colorant content
aqueous inks with especially small droplet size requires much more
ink materials to generate comparable final image output. This is
greater problem when the colorants used in the inkjet ink are not
soluble dyes, but are pigments or other insoluble colorants. High
color saturation and so called super saturation of the color image
may be difficult to achieve when using these inkjet inks.
[0005] One means of creating aqueous ink is adding viscosity
control agents that are high molecular weight natural synthetic
polymers, higher viscosity water soluble or miscible glycols, high
alcohols, accompanied by higher concentrations of colorants.
Several problems are associated with such simple approach. The use
of high molecular weight polymers may result in an aqueous system
that deviates from physical property requirements of the inkjet
printer used to print the ink, such as Newtonian fluid behavior.
Therefore, the ink improperly responds to the jetting mechanism.
The high molecular weight polymer in combination with increased
levels of colorants, especially non-soluble type of colorants, can
create clogging of the print head nozzles, even when using newer
print head technology designed for higher viscosity inks, since
such printers are not specifically designed for use with colorants
that are solids when printed.
[0006] Heat activated colorants have been used in digital inkjet
printing. The image quality is dependent on how effectively and
efficiently the heat activated colorants are transferred or fixed
to the substrate. Hale et al., U.S. Pat. No. 5,642,141 and Xu et
al., U.S. Pat. No. 5,488,907 teach inkjet printing methods using
finely divided heat activated dye solids. These methods incorporate
an ink having a viscosity generally around 2 to 4 cP at ambient
temperature. These patents do not specifically teach one how to
create a high transfer efficiency ink using heat activated dyes and
having relatively higher viscosity.
[0007] High viscosity inkjet inks may impose further problems for
heat activated inks when a high concentration of colorant is
present. Agents for controlling or modifying physical properties of
the ink may hinder the heat activation efficiency of the colorant,
due to high boiling points, affinity for the heat activated dye at
the activation temperature, or entrapment/encapsulation of the dye
particle due to the long polymeric chain structure of the
chemical/agent. These issues may be more pronounced when the
particle sizes of the colorants used in the inks are very small.
For example, a high concentration of glycerin may alter the heat
activation efficiency of a small dye particle under normal heat
activation temperature and duration. Further, a thickening agent,
such as carboxy methyl cellulose (CMC), may create a non-Newtonian
system, while also hindering activation or sublimation of the heat
activated dye.
[0008] Ink jet printer print heads, including Drop on Demand (DOD)
piezoelectric print heads, have of nozzles and orifices of varying
sizes. These nozzles and orifices dictate droplet size, print
speed, and jettable ink viscosity, and also the tolerance to
non-soluble colorants or polymeric particulates. An appropriate
range of dye particle sizes based on the nozzle or orifice size is
important when formulating the higher viscosity heat activated
inks.
[0009] There is a need for a higher viscosity ink that comprises
heat activated dye solids for digital printing, including transfer
printing or direct printing, that will not clog the print head,
will yield high heat activation efficiency, and be environmentally
safe, and which is suitable for high viscosity ink printers, which
is printers that require liquid inks having a viscosity of 5.0
centipoise or greater at ambient temperature.
SUMMARY OF THE PRESENT INVENTION
[0010] The present invention is a high viscosity inkjet ink that is
useful for printing heat activatable images using ink jet printers
such as Drop on Demand piezoelectric printers. The ink comprises
heat activated colorant solids that are not activated during the
inkjet printing process, and are printed onto a substrate in the
form of an image that can be activated and transferred to a
subsequent or final substrate by applying heat and intimate contact
between the two substrates. The ink can also be heat activated onto
the substrate without further transfer by applying heat at a
temperature that is suitable for the activation of the
colorant.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0011] The present invention is a liquid inkjet ink having a
preferred viscosity of not less than 5 cP, and may have a viscosity
from 6 to 100 cPs, with total water content of not less than 30% by
weight of the total ink formulation. A preferred viscosity range is
from 7 cP to 30 cP. A heat activated colorant is present in the ink
as printed in the form of solid particles or particulates. The
specific amount of the colorant(s) is supplied to achieve proper
color intensity and image quality upon heat activation. The
colorant is preferred to range from 1% to 15% by weight of the
total ink formulation.
[0012] In one embodiment, the ink contains a substantial amount of
viscosity control solvents/co-solvents such as diol, triol,
glycols, polyol, high alcohol, amines, polyamine, amino oxide, etc.
either alone or in mixture including but not limited to: glycerin,
ethylene glycol, diethylene glycol, triethylene glycol, propylene
glycol, dipropylene glycol, caprolactum, polyethylene glycol,
polypropylene glycol, urea, sorbitol, 2-pyrrolidinone,
N-methylpyrrolidinone, polyvinylpyrrolidinone (PVP),
polyvinylalcohol (PVA), gamma-butyrolactone (GBL),
2-methyl-1,3-propanediol, polyethylene polyamines, etc. These are
high viscosity water soluble or water miscible solvents/co-solvents
that will not substantially change the hydrophilicity of the ink
system, but which increase the viscosity of the ink. These
materials have little to no tendency to solubilize the heat
activated colorants. Furthermore, these solvents, co-solvents, or
viscosity control agents will not substantially alter the Newtonian
fluid behavior (incompressible) of the aqueous system. This
behavior may be expressed by the following equation:
.tau. ij = .mu. ( .differential. u i .differential. x j +
.differential. u j .differential. x i ) ##EQU00001##
[0013] with comoving stress tensor (also written as .sigma.)
ij = - p .delta. ij + .mu. ( .differential. u i .differential. x j
+ .differential. u j .differential. x i ) ##EQU00002##
[0014] where, [0015] .tau..sub.ij is the shear stress on the
i.sup.th face of a fluid element in the j.sup.th direction [0016]
u.sub.i is the velocity in the i.sup.th direction [0017] x.sub.j is
the j.sup.th direction coordinate
[0018] Other materials which may be used to adjust viscosity are
polypeptides such as abietoyl soy polypeptide, undecilenoyl soy
polypeptide, alcohol/glycol soluble prolamine, ethoxylated fatty
alcohol, ethoxylated fatty amine, acrylic amide, 2-ethyl-oxazoline
homopolymers, copolymer and/or terpolymers.
[0019] Depending on the specific viscosity requirement of the
printer and/or print head, viscosity control solvents/co-solvents
may weigh at least three times as much, and up to twenty times as
much, as the heat activated colorant solids of the total
formulation weight of the ink in order to maintain both high
viscosity and jettability. The total viscosity control
solvents/co-solvents may comprise between 15% and 60% of the total
formulation by weight.
[0020] Other ingredients may be used for stabilizing the colorant,
and for fine adjustment of the physical properties of the ink such
as surface tension, pH value, conductivity, and density. Further,
non-heat activated dyes and other colorants may be used in
combination with the heat activated colorant(s) to enhance image
quality and properties in certain applications. Self-dispersing
colorants, and/or pre-stabilized colorants may also be used.
[0021] Aqueous inkjet inks having the desired viscosity may have
different stabilization requirements, due to physical property
changes, such as ink density, Brownian movement of the
particulates, and electric conductivity. These changes impact the
particulate size distribution profile, and especially the upper
limit of the particle size distribution requirement. The following
empirical equation may be used for help selection of the upper
particle size distribution limit, if the particle size distribution
does not deviate substantially from a normal distribution
model:
.phi. .gtoreq. ( 5 D 1 - f ) 3 ##EQU00003##
[0022] where, [0023] .PHI. is the narrowest ink pathway inside the
print head such as nozzle/orifice diameter (in micron) [0024] D is
the particle size presented as 95% from total particle size
distribution (in micron) [0025] f is the colorant weight fraction
of the total formulation weight (<1) For example, a print head
having 35 micron nozzle/orifice diameter indicates a particle size,
at 95% distribution, of equal to or less than 0.62 micron in
diameter, if the colorants are 5% of the total weight. This formula
helps in creating an ink that will not clog the narrow path inside
the print head.
[0026] Heat activated colorants suitable for use may include
various disperse dyes or sublimation dyes that are activated or
sublimed by applying heat to the printed substrate or transfer
substrate. Generally, the heat activation temperature does not
exceed 450.degree. F., and most preferably, does not exceed
410.degree. F. Examples of colorants, in varying ratios, include
but are not limited, to C.I. Disperse Orange 13, 29, 31:1, 33, 49,
54, 55, 66, 73, 119 and 163; C.I. Disperse Red 4, 11, 54, 60 72,
73, 86, 88, 91, 92, 93, 111, 126, 127, 134, 135, 143, 145, 152,
153, 154, 159, 164, 167:1, 177, 181, 204, 206, 207, 221, 258, 278,
283, 288, 311, 323, 343, 348 and 356; C.I. Disperse Violet 33; C.I.
Disperse Blue 4, 13, 56, 73, 113, 128, 148, 154, 158, 165, 165:1,
165:2, 183, 197, 201, 214, 224, 225, 257, 266, 267, 287, 358, 359,
360, 379, Disperse Brown 26, 27; and Disperse Yellow 5, 42, 54, 64,
79, 82, 83, 93, 99, 100, 119, 122, 124, 126, 160, 184:1, 186, 198,
199, 204, 224 and 237. Depending on the specific application, other
organic and inorganic pigments, and soluble and insoluble dyes,
such as direct dyes, acid dyes, reactive dyes, vat dyes, cation
dyes, basic dyes, luco dyes, thermochromatic, and photochromatic
colorants may also be used.
[0027] The colorant will remain as a particulate in order to be
heat activated or sublimed. This is not a significant issue for
water insoluble colorants, such as sublimation dyes, in lower
viscosity applications where little to no glycol or other viscosity
increasing agents are present. The difference between the boiling
point of water and the ink heat activation temperature, which is
typically greater than 50.degree. F., indicates that activation or
sublimation of the ink solids will occur after the aqueous
components vaporize, so that activation or sublimation is not
materially hindered by these components of the ink.
[0028] The relatively high concentration of high boiling point of
glycols, polyol, and other viscosity control ingredients can create
a high boiling system which makes the activation or sublimation of
the colorants very difficult. The boiling point may be near, or
even above, the heat activation temperature of the dye, such as
within 20.degree. F. of the heat activation temperature. Particles
with smaller diameters may temporarily, or even permanently, bond
with these ingredients and not activate, due to hydrogen bonding,
entrapment, or forming a high boiling point co-boiling system.
Solvency of the non-polar portion of these ingredients may also
contribute to the hindering of the colorant, especially the outside
portion of the colorant particulates at a temperature near the
boiling point of these solvents or agents. Only the inside portions
of the colorant particles, which are not in contact with the "bulk"
ingredients of the ink, may activate or sublimate.
[0029] In one embodiment of the present invention the particulate
size of the heat activated colorants are limited so that sufficient
colorant molecules are be successfully activated or sublimated. The
following model is indicative of the particles sizes of the
dye:
d .gtoreq. 2 aT s 1 - K 1 / 3 ##EQU00004##
[0030] where, [0031] d is the minimum particle size in diameter (in
micron) to ensure heat activation efficiency K [0032] K is the heat
activation efficiency (K<1) [0033] Ts is the molecular size of
heat activated colorant in the longest dimension (in nanometer,
generally Ts=1.25) [0034] a is the solvency hindering impact
parameter, for high viscosity aqueous inks, a>1 For relatively
high viscosity inks having more than 20% by weight of high
viscosity solvent, a=3, meaning about three layers of molecules of
the colorant particulate may be hindered. Therefore, the
relationship between the particle size and heat activation
efficiency can be defined as:
[0034] d .gtoreq. 7.5 1 - K 1 / 3 ##EQU00005##
[0035] where, [0036] d is the minimum particle size in diameter (in
micron) to ensure heat activation efficiency K [0037] K is the heat
activation efficiency (K<1)
[0038] One embodiment of the invention has a heat activation
efficiency higher than 65% (K) for the colorant particulates.
Substantially all particles of the colorant having a diameter of
less than 50 nanometers are excluded from the ink. The low transfer
efficiency caused by the high concentration of the viscosity
control solvents/co-solvents to these particulates is thereby
substantially eliminated.
[0039] The present invention may be used with inkjet inks for
continuous inkjet, drop-on-demand thermal or bubble inkjet,
drop-on-demand piezo electric, ultrasonic or mechanical inkjet
printhead delivery systems. Physical properties of the ink may be
adjusted suitable for specific printhead requirements. A preferred
printer for printing an ink according to the invention is a RICOH
GELSPRINTER inkjet printer, which is designed to print OEM inks
having a viscosity of about 7. This printer is known in the
industry as a printer for high viscosity inks. Inkjet printers
designed for inks having a viscosity of 5.0 or greater are
preferred.
[0040] Heat activation is according to known processes for heat
activation of the dyes. For example, a heat press may be used to
activate and/or transfer inks comprising sublimation dyes according
to the teachings of Hale, U.S. Pat. No. 5,488,907.
[0041] The follow examples illustrate the general composition of
the high viscosity heat activated ink.
Example 1
[0042] An ink for use with a Ricoh GelSprinter ink jet printer,
nozzle size 35 microns, and having a viscosity of about 7.5
cPs:
TABLE-US-00001 [0042] Ingredient Weight % Disperse blue dye
(pre-stabilized) 3.5% Glycerin 40% Poly(2-ethyl-oxazoline) 2%
Non-ionic Surfactant 3.5% Proxel GXL 0.1% Other agents 2.0%
De-ionized Water balance
[0043] The ink according to the example is produced with an upper
limit (95%) of particles at 0.3 micron and a lower limit to 0.05
micron. Transfer printing of an image printed with the ink on
polyester fabric using 400.degree. F., with a 35 second heat
activation time produces an image having an optical density (cyan)
of 1.25 or greater as measured by an X-Rite densitometer.
Example 2
[0044] An ink for use with a Spectra Skywalker inkjet printer,
nozzle size 45 microns, and having a viscosity of about 15 cPs:
TABLE-US-00002 [0044] Ingredient Weight % Disperse dye mixture
(pre-stabilized) 5.6% CAB-O-JET .RTM. aq. Black pigment dispersion
1.5% Diethylene Glycol 20% e-caprolactam 15% Non-ionic Surfactant
3.5% Proxel GXL 0.1% Other agents 2.0% De-ionized Water balance
[0045] This ink has a particle upper limit (95%) at 0.6 microns,
and a lower limit to 0.05 microns. Direct printing onto
polyester/cotton (50/50) with heat activation of the dye at
410.degree. F., at 30 seconds, produces an image with an optical
density of 130 or greater as measured by an X-Rite
densitometer.
* * * * *